The parameters governing the response time of a system to follow transient changes of conductivity caused by short pulses of radiation are discussed, and designs for coaxial conductivity cells with parallelhyphen;plate electrodes to obtain subnanosecond time resolution are described. The performance of the system is evaluated using ionization pulses of 30hyphen;ps width. This yields values in agreement with theory: 95 ps for the rise time and 80 ps for the fall time with virtually no signal distortion. Ways to decrease these times further are discussed.
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